The present invention relates to an optical sensor device for recognizing optical irradiation and detecting its direction, and, more particularly, to an optical sensor device which measures transit time and determines signals by comparison of amplitudes.
DE-PS 33 23 828 and DE-OS 35 25 518 disclose sensors in which the direction of the incident laser irradiation is detected and determined by measurement of the transit time. In this case, the laser irradiation is guided in optical fibers. A very small number of detector elements and electronic circuits detect a large solid angle with a good angular resolution. However, this approach requires optical fibers which can operate in the whole spectral region of a possible laser threat.
In the range of from 0.4 .mu.m to 2 .mu.m, which detects the most frequent laser sources, such as ruby lasers, laser diodes, alexandrite lasers, Nd:YAG lasers, erbium and holmium lasers, etc., silicone dioxide glass fibers may be used. For bridging the range up to 4.5 .mu.m, for example, in connection with deuterium fluoride laser (at 4.2 .mu.m), optical fibers consisting of fluorides--such as zirconium fluoride--have been found to be suitable.
None of the mentioned optical glass fibers have, however, transmission properties which can be used in the militarily important spectral ranges of from 8 .mu.m to 14 .mu.m. In recent years, other types of optical fibers have been developed, such as fibers used as wave guides made of plastic materials and metals; fibers made of crystalline salts, such as NaCl, KCl; polycrystalline fibers consisting of Cs Br, Tl Ce, or chalcogenidic fibers consisting of AS, Ge, Se, Te. In comparison to optical fibers for the shorter wavelengths, however, the above-mentioned newer fibers still have considerable disadvantages, specifically high damping and susceptibility to moisture, toxicity which cannot be ignored and low flexibility. For this reason, it has not been possible to build laser warning sensors which can operate without any problems in the spectral range of from 8 .mu.m to 14 .mu.m.
It is an object of the present invention to provide a sensor which operates without any fibers or, at most, with those of short length and permits good angular resolution with a small number of detector elements also in a wide IR-range. Another object of the present invention is to provide such a sensor in which also a compact construction ensures a high optical sensitivity while, at the same time, being insensitive with respect to background light and scintillation of the laser beam in the atmosphere, and having a large dynamic range.
The foregoing objects have been achieved by constructing a sensor input lens system as a dielectric transparent spherical-shell section. In an embodiment, the shell surfaces of the section can comprise a thin shell surface, an air space or vacuum gap, and a totally reflecting mirror surface guiding incident irradiation by reflection to the edge of the spherical-shell section and from there directly to several electro-optical detectors so as to determine the direction of incidence from the relationship of the signals of the detectors. In another embodiment, the interior surface of the shell section can be vaporized so as to form a mirror which reflects impinging irradiation to the edge of the spherical-shell section.